This invention relates to sensor assemblies for color optical image scanners, optical scanners, and methods of scanning color images.
Color optical scanners produce color image data signals representative of an object or document being scanned by projecting an image of the object or document onto an optical photo sensor array. The color image data signals may then be digitized and stored for later use. For example, the color image data signals may be used by a personal computer to produce an image of the scanned object on a suitable display device, such as a CRT.
A typical optical scanner comprises illumination and optical systems to illuminate the object and focus a small area of the illuminated object, usually referred to as a xe2x80x9cscan line,xe2x80x9d onto the photo sensor array. The entire object is then scanned by sweeping the illuminated scan line across the entire object, either by moving the object with respect to the illumination and optical assemblies or by moving the illumination and optical assemblies relative to the object.
A typical illumination system for a color scanner may include a suitable white light source, such as a fluorescent or incandescent lamp, to illuminate the object. A typical optical system may include a lens assembly to focus the image of the illuminated scan line onto the surface of the optical photo sensor array and may also include one or more mirrors to xe2x80x9cfoldxe2x80x9d the path of the light beam, thus allowing the optical system to be conveniently mounted within a relatively small enclosure.
While various types of photo sensor devices may be used to detect the light from the illuminated scan line, a commonly used sensor is the charge coupled device or CCD. A typical CCD may comprise a large number of individual cells or xe2x80x9cpixels,xe2x80x9d each of which collects or builds-up an electrical charge in response to exposure to light. Since the size of the accumulated electrical charge in any given cell or pixel is related to the intensity and duration of the light exposure, a CCD may be used to detect light and dark spots on an image focused thereon. In a typical scanner application, the charge built up in each of the CCD cells or pixels is measured and then discharged at regular intervals known as sampling intervals, which may be about 5 milliseconds or so for a typical scanner.
Color optical scanners of the type described above usually operate by collecting multiple color component images of the object being scanned. For example, data representative of red, green, and blue color components of the image of the scan line may be produced, correlated, and stored by the scanner apparatus. The particular color components, e.g., red, green, and blue, are commonly referred to as primary colors, primary stimuli, or simply, primaries.
As is well-known, various combinations of three such primary colors can be used to produce any color stimulus contained within the gamut of colors on the CIE chromaticity diagram that lie within the triangle of primaries. The amounts of each primary color required to match a particular color stimulus are referred to as tristimulus values. Written mathematically: C=r(R)+g(G)+b(B) Put in other words, a given color stimulus C (e.g., the image of the scan line) can be matched by r units of primary stimulus R(red), g units of primary stimulus G (green), and b units of primary stimulus B (blue). All the different physical stimuli that look the same as the given color stimulus C will have the same three tristimulus values r, g, and b. Thus, it is possible to match a color stimulus by a mixture of three primary colors or stimuli, with the tristimulus values r, g, and b determining the required amount of each primary color. It is important to keep in mind that the foregoing method will only achieve psycho physical color match (i.e., the color will appear the same to the human eye), as opposed to a physical or spectral match.
Many different techniques have been developed for collecting data representative of multiple color component images (i.e., the tristimulus values) of the object being scanned. One technique is to project the image of the illuminated scan line onto a single linear photo sensor array. However, in order to collect the multiple color component images (i.e., the tristimulus values) of the illuminated scan line, a different color light source (a primary) is used to illuminate the scan line on each of three scanning passes. For example, the object first may be scanned using only red light, then only green light, and finally only blue light. The output signal from the photo sensor for each color thus represents the tristimulus value for that color. In a variation of this technique, three scanning passes may be made using a white light source, but the light from the illuminated scan line is filtered by a different color filter during each of the three passes before being focused onto the optical photo sensor array. Either way, the tristimulus values for the primaries (i.e., the red, green, and blue colors) may be determined from the output signal of the photo sensor.
Another technique, described in U.S. Pat. No. 4,709,144 issued to Vincent and U.S. Pat. No. 4,926,041, issued to Boyd, et al., both of which are hereby specifically incorporated by reference for all that is disclosed therein, is to split the illuminated (i.e., polychromatic) scan line into multiple color component beams, each of which are then focused onto multiple linear photo sensor arrays. For example, the illuminated scan line may be split into red, green, and blue color component portions which are then simultaneously projected onto three (3) separate linear photo sensor arrays. The output from each photo sensor represents the tristimulus value for the corresponding primary. This technique allows the tristimulus values from any particular scan line to be generated simultaneously, thus allowing easier correlation of the image data for each separate primary.
Regardless of the particular technique used to collect the tristimulus values, the color accuracy of the reproduced image will be only as good as the spectral band match between the spectral sensitivity of the photo sensor used to record the image and the spectral sensitivity for human vision. As is well-known, the human eye comprises three different kinds of color receptors (cones) that are sensitive to various spectral bands or regions that roughly correspond to red, green, and blue light. The receptors are relatively xe2x80x9cbroad bandxe2x80x9d devices, sensitive to a wide range of wavelengths with each color band region. For example, blue receptors are typically sensitive to light having wavelengths ranging from about 400 nm to 500 nm; green receptors to light having wavelengths ranging from about 480 nm to 600 nm; and red receptors to light having wavelengths ranging from about 500 nm to 650 nm. While the specific sensitivities of the color receptors vary from person to person, the average response for each receptor has been quantified and is known as the xe2x80x9cCIE standard observer.xe2x80x9d
One problem which continues to present challenges is associated with the fact that during scanning of an object, one of the scanner or the object is typically moving relative to the other. Accordingly, where exposure takes place in a sequential manner as, for example, with a single array sensor, transitions from one color to another color on the object (i.e., from black-to-white where, for example, a portion of a printed letter appears on a page) occurs at different times as seen by the sensor. Hence, a halo effect can be presented whereby the ultimately-rendered image, such as a printed image of the scanned object, will be seen to have a halo adjacent to the transition regions. Specifically, and with reference to FIG. 11, an enlarged CIS (Contact Image Sensor) scan of the word xe2x80x9cYouxe2x80x9d appears. The word xe2x80x9cYouxe2x80x9d was scanned from an object on which the letters were black and the background was white. The background, however, appears as yellow and there are vertical lines which run through much of this image. Each square in the image represents a single pixel value. A linear array of sensors view a horizontal line which cuts across the word xe2x80x9cYouxe2x80x9d from left to right, then the line moves down (toward the bottom of the word) and scans another horizontal line. In this example, the top edge of the horizontal line (at the tops of the individual letters) appears as yellow. The bottom edge of the letters appear as blue. This is not the case for vertical lines defining the sides of the letters, which do not have a different color on the left side versus the right side. The above-described color artifact is undesirable because the ultimately-rendered image is not as accurately presented as is desirable.
Accordingly, this invention arose out of concerns associated with providing improved scanner assemblies, optical scanners, and methods of scanning color images.
Sensor assemblies, optical scanners, and methods of scanning color images are described. In one embodiment, a single array of sensor elements is provided. A light source assembly is positioned in proximity with the single array and is configured to illuminate an object with a plurality of different colors of light while at least one of the object or the single array moves with a velocity having a velocity profile relative to the other object or the single array. An illumination sequence processor is operably coupled with the light source assembly and is configured to assign individual colors of light for illumination on the object in accordance with variations in the velocity profile of the velocity with which the object or the array moves relative to the other.
In another embodiment, an array of sensor elements is provided. A light source assembly is positioned in proximity with the array and is configured to sequentially illuminate an object with a plurality of different colors of light. Responsive to such illumination, the array is configured to receive light which is sequentially reflected from an illuminated object, and to provide data which can be arranged into a plurality of color planes. The color planes are individually indicative of the sequentially reflected light. A color plane manipulation processor is operably coupled with the array and is configured to adjust the relative position of at least one of the color planes relative to another of the color planes. Accordingly, such provides improved color data describing portions of an object illuminated by the light source assembly.
In another embodiment, a method of scanning color images includes providing a single array of sensor elements. A multi-color light source assembly is provided and is positioned in proximity with the single array. At least one of an object or the single array is moved relative to the other of the object or the single array with a velocity having a velocity profile. The object is selectively illuminated using the multi-color light source assembly by providing sequenced individual colors of light in accordance with and responsive to variations in the velocity profile. Light reflected from the object is detected responsive to the illuminating thereof.